Common problems when measuring pressure differences in low velocity systems as air ventilation system are the low column heights and satisfying accurately. The pressure difference in a inclined u-tube can be expressed as:
pd = ÃÂ³ h sin(ÃÂ¸) (2), where
h = length, difference in position of the liquid column along the tube (mm, ft)
ÃÂ¸ = angle of column relative the horizontal plane
Inclining the tube manometer will increase the accuracy of the measurement.